This invention relates to processes for preparing articles for use in rubber reinforcement. More particularly, it relates to the preparation and treatment of brass-plated steel wire as reinforcing material for vulcanized rubber articles such as tires.
The problem of securing adequate adhesion of rubber to metal has been investigated extensively by those skilled in the various aspects or rubber manufacturing. The best known reference on this subject, Buchan, Rubber Metal Bonding (Crosby, Lockwood & Son, London, 1948) describes the now widespread practice of vulcanization of rubber onto a brass-plated metal substrate. This practice facilitates the drawing of the wire to the very small diameters used in rubber reinforcement, and it helps to assure adhesion of the wire to the rubber mix in which the wires are encased.
It is generally agreed by those skilled in the art that adhesion of rubber to brass-plated steel wire is dependent upon a bond between the copper in the brass and the sulfur in the rubber. The growth of an oxide layer at the surface of the wire is detrimental to good adhesion potential.
The oxide layer in fact begins growing during the wire plating and drawing process. The present invention is directed specifically toward control of surface oxide layer during the plating and drawing process.
A variety of processes for treatment of rubber reinforcing wire are disclosed in the prior art. Coating systems for the wire constitute a significant portion of the prior art in this field. U.S. Pat. No. 3,749,558 describes the coating of steel wire with nickel followed by copper and zinc which are transformed into brass in situ by heating. The nickel is to improve corrosion resistance.
Two patents directed to tire bead wire applications are U.S. Pat. No. 2,870,526 (wire plated with zinc then brass) and U.S. Pat. No. 2,939,207 which discloses wire of a ferrous base coated first with zinc; second, with a thin barrier coating of nickel, cobalt or antimony; and coated thirdly with a rubber adherent material selected from the group copper, copper zinc alloy, copper cadmium alloy, or copper tin alloy.
Canadian Pat. No. 976,858 discloses rubber reinforcing wire plated with brass on top of which there is a second plating of tin or lead, which second coating imparts improved adhesion to the wire.
Two French Pat. Nos. 1,174,055 and 71704 disclose steel wire coated first with zinc, then with copper and finally heat treated.
A method of coating copper plated elements with zinc is disclosed in U.S. Pat. No. 3,597,261. This patent pertains to the coating of copper tubing, in particular, that tubing which is used for automobile brake lines.
Zinc phosphate coatings are discussed in two publications: WERKSTOFFE und KORROSION 25 Jahrg. Heft May, 1974, p pages 327-330, the article "Untersuchungen uber die Bildung der Zinc-Phosphatuberzuge und ihre Korrosionsschutzeigenschaften" (INVESTIGATIONS ON THE FORMATION OF ZINC-PHOSPHATED COATINGS AND THEIR CORROSION PROTECTION PROPERTIES) by Chr. Kosarev of ZSMK (Central Institute for Corrosion protection of Metals) in Bulgaria and WIRE WORLD INTERNATIONAL Vol. 15, 1973, page 104-110, the article "ZINC PHOSPHATE COATINGS FOR FORMED COMPONENTS MADE OF STEEL, ZINC AND ALUMINUM."